Native ESM module support

[jfparadis]

• Rollup Version: 1.27.5
• Operating System (or Browser): MacOS
• Node Version (if applicable): v13.6.0
• Link to reproduction (IMPORTANT, read below): https://github.com/jfparadis/rollup-esm-test

Module support in node is still in early stages (and maybe not ready for runtime), but there are benefits to use it in a tool chain, and to begin creating packages with native support:

• to get the native behavior of JS in tests
• to avoid caching issues with esm transpilation

Numerous options are possible as documented here:
https://github.com/nodejs/node/blob/master/doc/api/esm.md#approach-1-use-an-es-module-wrapper

Expected Behavior

This form should be usable from a package with native ESM support:

import { rollup } from 'rollup';

As verifiable via a simple command-line test:

node  --input-type=module -e "import { rollup } from 'rollup'; console.log(typeof rollup)"
function

Or as verifiable in context of the test package provided:

git clone https://github.com/jfparadis/rollup-esm-test.git
cd rollup-esm-test
npm install

npm test

# rollup
ok 1 should be equal

1..1
# tests 1
# pass  1

# ok

Actual Behavior

Error, as verifiable via a simple command-line test:

node  --input-type=module -e "import { rollup } from 'rollup';"
import { rollup } from 'rollup';
         ^^^^^^
SyntaxError: The requested module 'rollup' does not provide an export named 'rollup'

Or as verifiable in the context of the test package provided:

git clone https://github.com/jfparadis/rollup-esm-test.git
cd rollup-esm-test
npm install
npm test
import { rollup } from 'rollup';
         ^^^^^^
SyntaxError: The requested module 'rollup' does not provide an export named 'rollup'

Workaround

The workaround is to use a wrapper or an alternate syntax to resolve the exports:

import cjsRollup from 'rollup';
const { rollup } = cjsRollup;

As verifiable via a simple command-line test:

node  --input-type=module -e "import cjsRollup from 'rollup'; const { rollup } = cjsRollup; console.log(typeof rollup)"
function

Or as verifiable the in context of the test package provided, by commenting and uncommenting a few lines in test.js.

[lukastaegert]

Approach 2 https://github.com/nodejs/node/blob/master/doc/api/esm.md#approach-2-isolate-state actually sounds like a reasonable way forward. I would like to avoid importing CJS parts in the ESM parts of Rollup to provide an optimized build for JS API consumers and re-bundlers of Rollup, and I think it is reasonable to consider Rollup to be stateless enough. We could do this for Rollup 2. If it works correctly on Node 10, we are good to go.

[lukastaegert]

Ok, I really would love to support this but at the moment, acorn is being a huge pain here: acornjs/acorn#824 (comment)

Basically I need to rewrite my code several times to use named imports for the browser build but default imports for the Node builds to make sure even the ESM version of Rollup pulls in the CJS version of acorn.

[lukastaegert]

Solved in rollup@2.0.0